 /*******************************************************************************
  * Copyright (c) 2007 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  ******************************************************************************/

 package org.eclipse.ui.internal.navigator;

 import java.util.HashMap ;
 import java.util.Map ;

 import org.eclipse.ui.internal.navigator.extensions.ExtensionStateModel;
 import org.eclipse.ui.navigator.IExtensionStateModel;
 import org.eclipse.ui.navigator.INavigatorContentDescriptor;
 import org.eclipse.ui.navigator.INavigatorContentService;

 /**
  *
  * A content extension may have its content and label providers disposed
  * whenever the extension is activated or deactivated. However, the state model
  * lives throughout the life of the viewer to allow Action Providers to drive
  * their behavior from it.
  *
  * @since 3.3
  *
  */
 public class NavigatorExtensionStateService {

     private final Object lock = new Object ();
     private INavigatorContentService contentService;

     /**
      * Create an ExtensionStateServie that will keep track of the state models
      * of content extensions.
      *
      * @param theContentService
      * The content service which manages this state model service.
      */
     public NavigatorExtensionStateService(INavigatorContentService theContentService) {
         contentService = theContentService;
     }

     /*
      * A map of (String-based-Navigator-Content-Extension-IDs,
      * NavigatorContentExtension-objects)-pairs
      */
     private final Map /* <INavigatorContentDescriptor, IExtensionStateModel> */stateModels = new HashMap ();

     /**
      * Return the state model for the given descriptor.
      *
      * @param aDescriptor A content descriptor
      * @return The state model for the given descriptor.
      */
     public IExtensionStateModel getExtensionStateModel(
             INavigatorContentDescriptor aDescriptor) {
         synchronized (lock) {
             IExtensionStateModel model = (IExtensionStateModel) stateModels
                     .get(aDescriptor);
             if (model == null)
                 stateModels.put(aDescriptor, model = new ExtensionStateModel(
                         aDescriptor.getId(), contentService.getViewerId()));
             return model;
         }
     }

 }

